Spectral quality influence on in vitro morphophysiological responses of Eucalyptus dunnii Maiden and Eucalyptus grandis W.Hill ex Maiden × E. urophylla S.T.Blake

Background: In vitro growth and development of plants in the micropropagation stages are influenced by several factors, including the light spectral quality, which has shown important effects on the photomorphogenesis. The work aimed to evaluate the photomorphogenic effect of spectral qualities on in vitro culture of Eucalyptus dunnii and Eucalyptus grandis × E. urophylla. Methods: Six light spectral qualities (i.e., red, white, blue, yellow, purple, and green) on in vitro multiplication, elongation, and adventitious rooting stages were evaluated through analysis of variance followed by a Tukey’s test. Results: White spectral quality was most adequate for in vitro multiplication of Eucalyptus dunnii and Eucalyptus grandis × E. urophylla, as it resulted in less tissue oxidation, longer shoot length, and more buds per explant. Red, blue and yellow spectral qualities increased the chlorophyll a, chlorophyll b, and total chlorophyll (a+b) leaf contents of Eucalyptus dunnii. To promote in vitro elongation, white spectral quality was most suitable for Eucalyptus dunnii, and yellow for Eucalyptus grandis × E. urophylla, as these resulted in more shoot length and shoots per explant. Red, white, blue and purple spectral qualities increased the stomatal density of Eucalyptus dunnii; while the white and yellow were the better for Eucalyptus grandis × E. urophylla. To promote in vitro rooting, the white and yellow spectral qualities caused the best results for the Eucalyptus dunnii and Eucalyptus grandis × E. urophylla, with longer root length and more roots per explant. Eucalyptus dunnii showed reduced adventitious rooting, regardless of spectral quality. Conclusions: Light quality influence the morphophysiological responses of Eucalyptus in different stages of in vitro culture. Our results contribute to maximise the in vitro cloning of important eucalypts species.